Name Period Date Chapter 8 nergy Work and Power … · Chapter 8 nergy Work and Power ... A car is traveling on a level road at 16.67 m/s, ... If the car starts from rest, what is
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E5. An 8 kg mass is lifted from the floor to the ceiling in a science room using a small electric motor that puts out 25 watts of power. If it takes 7 seconds to lift the mass to the ceiling, calculate the work done on the mass and the height of the science room.
Record all givens, draw a picture, arrow all vectors, write the formula, substitute and solve
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unitsa) unitsb) E6. A monkey has bought a piano but lives on the sixth-story of an apartment building
and needs to get the piano from the street 15 meters up to his flat. The piano will not fit through the doors into the apartment but will fit through the outside window. The monkey attaches a rope to the piano and the other end to a 1,750 watts motor attached to the top of the building. How much energy will it take to lift the 285 kg piano to the monkey’s flat and how long will it take?
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E7. A monkey is trying out his new Porsche. The monkey wants to “feel” the vehicles acceleration. Starting from rest the monkey pushes the gas pedal to the floor and the car goes from 0-60 mph (0-26.82 m/s) in 3.4 seconds. If the mass of the car is 1,361-kg calculate the change in kinetic energy and the power output of the Porsche.
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unitsa) unitsb) E8. A car is traveling on a level road at 16.67 m/s, the engine generates 12 hp (8948.4
watt). Determine the average retarding force due to wind resistance and friction.
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3. A gorilla, a champion weight-lifting, raises 240 kg of weights a distance of 2.35 meters in 2.5 seconds. Calculate the work done lifting the weight and the power output.
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unitsa) unitsb) 4. A load of bricks, mass is 420 kg, is to be lifted by a winch to a height of 120 meters
taking 5.0 minutes. Calculate the minimum power of the winch motor.
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7. A monkey puts out 25 watts of power pushing horizontally on a crate with a force of 100 N in order to move the crate a distance of 15 meters. Calculate the work done by the monkey and the time it takes to do the work.
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unitsa) unitsb) 8. A manually operated winch is used to lift a 200 kg mass to the roof of a 10 meters
tall building. Assuming that you can work at a steady rate of 200 W, how long will it take you to lift the object to the roof?
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9. A car of mass 1550 kg can reach a speed of 60 mph (26.8 m/s) in 7.1 s. Calculate the change in kinetic energy and the average power needed to accomplish this.
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unitsa) unitsb) 10. A shot-putter accelerates a 7.30-kg shot from rest to 14.0 m/s. If this motion takes
2.00 seconds, what average power was supplied?
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17. A car of mass 942.4 kg accelerates from rest with a constant power output of 140.5 hp. Neglecting air resistance, what is the speed of the car after 4.55 s?
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unitsa) 18. A 20-hp motor is used to lift an elevator whose mass, when empty, is 1200 kg. If
this elevator should rise at 1 m/s what is the maximum additional load that can be placed in it, if all friction losses are neglected?
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19. An 1800-kg car is equipped with a 40-hp engine. Neglecting all friction losses, determine the maximum speed at which this car can climb a 15° grade.
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unitsa) 20. A bicyclist coasts down a 7.0° slope at a steady speed of 5.0 m/s. Assuming a total
mass of 75 kg (bicycle plus rider), what must the cyclist’s power output be to pedal up the same slope at the same speed?
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